JPH0920712A - Production of 2-substituted cyclopentanone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain the subject compound by reacting an adipic ester with an alkoxide in the presence of an inactive solvent, alkylating the product without isolating the product, and subsequently hydrolyzing and decarbonating the alkylation product with an acid and heat.

SOLUTION: An adipic ester of formula I (R₂ is a linear or branched 1-10C alkyl, a 7-12C aralkyl, etc., which may be substituted by uppermost three specific substituents) is reacted with an alkoxide of the formula: M(OR³)_n [M is an alkyli (alkaline earth) metal; R³ is a 1-10C alkyl, etc.; (n) is 1, 2] in an inactive solvent, and the obtained cyclopentanone-2-carboxylic ester salt of formula II (M is the monovalent metal among the above-described metals) is alkylated with an alkylating agent without isolating the salt of formula II. The obtained 2-alkyl-cyclopentanone-2-carboxylic acid ester of formula III is not isolated and thermally hydrolyzed and decarbonated in the presence of an acid to obtain the 2-substituted cyclopentanone of formula IV.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a process for preparing 2-substituted cyclopentanones, especially 2-methylcyclopentanone, from dialkyl adipates.

[0002]

It is already known to prepare 2-substituted cyclopentanones by alkylation of cyclopentanone-2-carboxylic acid esters, followed by hydrolysis and decarboxylation. This method has several drawbacks. Starting from a dialkyl adipate, this method has three steps, and even the best method described in the literature only produces 40-45% of theory. Thus, the cyclization in the case of the ethyl ester leads to an isolated yield of 70-78% and in the case of the methyl ester 68-74%.
Leading to isolated yield of (J.prakt.Chem.4th series, Volume
9, page 43 (1959)). Then methyl 2-
Alkylation with, for example, methyl bromide to obtain methylcyclopentanone-2-carboxylate proceeds in a yield of about 70% of theory and subsequently about 80% of theory.
Hydrolysis and decarboxylation of yields up to 42% of theory based on the dialkyl adipate used (Chem B
er. 80 , 202 (1974)).

The reason for the low yield is the reversibility of the first stage cyclization and the cleavage that occurs for the same reason in the carbanion formation in the alkylation stage due to the base alkoxide of the auxiliary. The α-alkyl adipates are formed by reversible cleavage and the compounds themselves cyclize to give the undesired 5-alkyl-cyclopentanone-2-carboxylic esters (J. Org. Chem. 29 , 2782 ( 1964)).

A further decrease in yield is also caused by the O-alkylation of mesomeric enolate ions, the extent of which depends largely on the nature of the alkali metal counterion, solvent and alkylating agent. Thus, the inexpensive and frequently used alkyl chlorides and alkyl sulfonates lead exactly to the formation of O-alkyl derivatives, which, by vigorous acid hydrolysis and subsequent decarboxylation, produce cyclopentanone, Isolation, which is usually done by distillation, requires effort to perform the separation. Therefore, expensive alkyl bromides and alkyl iodides, which require complex operational safety measures, are commonly used in alkylation reactions.

Another disadvantage of these processes is the notable water solubility of the final product, which is especially pronounced in the case of 2-methylcyclopentanone. This means that the product must be laboriously isolated from the aqueous reaction mixture by multiple extractions and the organic extract must be dried and distilled. The remaining aqueous phase is contaminated with organic material and requires special treatment and disposal.

In order to alkylate 2-carboalkoxy-cyclopentanone with the corresponding alkyl halide, dimethyl sulfoxide (J.Org.Chem. 32 , 4067 (196
Dipolar aprotic solvents such as 7)) and acetone (SYNTHESIS 1973 , 316) are described in the literature as advantageous. Because in other non-polar solvents such as benzene or toluene, ion-pair macromolecule aggregates are present, which react undesirably as they contain significant free enolate ions (J. Am. Chem. Soc. 82 , 2895
(See (1960)).

Here too, alkyl iodides or alkyl bromides must be used, in the case of bromides O-
The alkylation rate is quite high. Higher O-alkylation is expected when using alkyl chlorides, which makes the process even more uneconomical. Furthermore, in order to remain a single-step modification, a special reaction with the potassium salt of cyclopentanone-carboxylic acid ester is described, which must be carried out with the more expensive potassium alkoxide. It will be. Otherwise, the necessary solvent changes would make the process even more uneconomical. The use of dipolar aprotic solvents is generally
The following work-up changes are necessary: After the reaction is complete, the alkylation batch is diluted with water and the product is extracted with a non-polar solvent such as ether or a hydrocarbon. As already discussed above, more extraction is needed due to the polarity of the product and recovery of the solvent used is generally miscible with water, and highly organically contaminated effluents are typically produced. It is very complicated.

The hydrolysis of 2-alkylcyclopentanone-2-carboxylic acid ester can proceed only under acidic conditions because the side reaction of acid cleavage (ring opening) is too remarkable under alkaline conditions. To achieve a reasonable reaction time, a strong acid must be used in acid hydrolysis. That is, for example, diluted perchloric acid (Ber, 80 , 202 (1
974)) or concentrated hydrochloric acid (Bl.Soc.chim.Bel
g. 35, 315 a should be in the reference) is used, both it is expensive, and the reason that higher corrosion resistance,
Less convenient than diluted sulfuric acid.

In addition to the most general method described above, there are many more methods for the preparation of 2-alkylcyclopentanones, especially 2-methylcyclopentanone.

For example, cyclization of α-methyladipic acid to form an anhydride, followed by its thermal decomposition (see Cr 144 , 1357), distillation of the calcium salt of this acid, and cyclopentanone Direct alkylation, however, results in an almost inseparable mixture of mono-, di- and trimethylcyclopentanones and proceeds only with strong auxiliary bases such as sodium amide.

From 1-methylcyclopentene oxide, for example Grignard compounds (Soc. Chim. Belg. 37 , 151), formic acid / sulfuric acid (see Am. Soc. 70 , 4139 (1948)).
The 2-alkylcyclopentanone can be obtained by treatment with or by passing steam over aluminum oxide at 300 ° C.

2-Chloro-1-methyl-cyclopentan-1-ol has also been reacted with Grignard compounds (see Cr 209 , 499 (1939)) or with alkali (Am.
c. 96 , 2783 (1934)).

Various 2-alkylidene-cyclopentanones can also be reduced.

All of these processes start with hard to obtain starting materials, use reagents which are only industrially difficult to handle, and are often non-selective and of low yield. An alternative method is the alkylation of 1-pyrrolidinocyclopentene (J. Heterocycl. Chem.
28, 1293 should be in the (1991)), which also total 3-
The process synthesis gives a yield of only 49% of theory based on cyclopentanone, which itself has to be prepared again from the adipic ester.

[0015]

[Constitution of Invention] This time, the formula

[0016]

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Wherein R ¹ represents a straight-chain or branched C ₁ -C ₆ -alkyl, C ₃ -C ₇ -cycloalkyl, or unsubstituted or halogen-substituted C ₇ -C ₁₂ -aralkyl. A process for the production of substituted cyclopentanones was found, which has the formula

[0018]

[Chemical 6]

Wherein the ^two R ² are the same or different and each is halogen and C ₁ -C ₆ -alkyl, C ₁ -C
Linear or branched C ₁ -C ₁₀ -alkyl, C ₇ -C, optionally substituted with up to three identical or different substituents selected from the group consisting of ₆ -alkoxy and nitro groups. ₁₂ -aralkyl or optionally up to three identical or different substituents selected from the group consisting of halogen and C ₁ -C ₆ -alkyl, C ₁ -C ₆ -alkoxy and nitro groups An adipic acid ester of C ₆ -C ₁₀ -aryl, which may be substituted, is represented by the formula (II
I) M (OR ³ ) _n (III) In the formula, M represents an alkali metal or an alkaline earth metal, R ³ is C ₁ -C ₁₀ -alkyl, C ₃ -C ₁₀ -cycloalkyl or C ₇ -C Represents ₁₂ -aralkyl, and n is M
Depending on the valence of the alkoxide of 1 or 2 is reacted in this manner to give a compound of formula (IV)

[0020]

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Wherein R ² has the meaning given to formula (II) and M represents a monovalent alkali metal or alkaline earth metal, a salt of a cyclopentanone-2-carboxylic acid ester of Got
Without isolation it is of formula (V) R ¹ -X (V) where R ¹ has the meaning given to formula (I), X is halogen, C ₁ -C ₆ -alkyl sulfonate, Or alkylating with an alkylating agent of C ₆ -C ₁₀ -aryl sulfonate, optionally substituted with up to two C ₁ -C ₄ -alkyl groups, thus giving formula (V
I)

[0022]

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Wherein R ² has the meaning given to formula (II) and R ¹ has the meaning given to formula (I) The acid ester is characterized in that it is hydrolyzed and decarboxylated by acid and heat treatment without isolation.

Halogen preferably represents chlorine or bromine, especially chlorine.

Suitable adipic acid esters of formula (II) are:
Wherein the ^two R ² groups are the same and are optionally linear or branched with up to two substituents selected from the group consisting of halogen atoms and C ₁ -C ₄ -alkyl groups. Branched C ₁ -C ₆ -alkyl, benzyl, or phenyl, which may be optionally substituted by up to two substituents selected from the group consisting of C ₁ -C ₄ -alkyl and nitro. is there.

Particular preference is given to those compounds of the formula (II) in which the ^two R ² radicals are identical and represent a straight-chain C ₁ -C ₄ -alkyl.
Adipic acid ester. Particularly suitable are dimethyl adipate and diethyl adipate.

Suitable alkoxides of the formula (III) are those in which M represents sodium, potassium, lithium, calcium or magnesium and R ³ is straight-chain or branched C ₁ -C ₆ -alkyl, C _3-. Represents C ₇ -cycloalkyl or benzyl. Particularly suitable are sodium methoxide, potassium methoxide, calcium methoxide and magnesium methoxide, sodium ethoxide, potassium ethoxide, calcium ethoxide, and magnesium ethoxide, sodium n-propoxide, potassium n-propoxide, calcium. n-propoxide and magnesium n-propoxide, sodium i-propoxide, potassium i-propoxide, calcium i-propoxide, and magnesium i-propoxide, sodium n-butoxide, potassium n-butoxide, calcium n- Butoxide and magnesium n-butoxide,
Sodium i-butoxide, potassium i-butoxide, calcium i-butoxide, and magnesium i-butoxide, sodium sec-butoxide, potassium sec-
Butoxide, calcium sec-butoxide, and magnesium sec-butoxide, sodium t-butoxide, potassium t-butoxide, calcium t-butoxide, and magnesium t-butoxide, and sodium pentoxide and potassium pentoxide, sodium hexoxide, and potassium hexoxide. Soxides, sodium cyclopentoxide and potassium cyclopentoxide, sodium cyclohexoxide and potassium cyclohexoxide, and sodium benzoxide and potassium benzoxide. Particularly preferred are:
Sodium methoxide and potassium methoxide, sodium ethoxide and potassium ethoxide, sodium i-propoxide and potassium i-propoxide and sodium t-butoxide and potassium t-butoxide.

Suitable inert solvents for the reaction of adipic acid esters with alkoxides are, for example, aliphatic and aromatic hydrocarbons with a boiling point (at atmospheric pressure) of at least 80 ° C. As examples there may be mentioned heptane, octane, nonane, decane, isododecane, benzene, toluene, cumene, xylene, di- and triisopropylbenzene and halogen, and / or chlorobenzene, dichlorobenzene, trichlorobenzene, anisole, phenetole. And C ₁ -C ₄ -alkoxy-substituted aromatic hydrocarbons such as phenyl isopropyl ether. Any mixture of these solvents can also be used.

Dipolar aprotic solvents such as dimethyl sulfoxide, tetramethylene sulfone, di-C ₁ -C _6- (cyclo) -alkylformamide,
N-C ₁ -C ₆ -alkylpyrrolidone, -piperidone and / or -caprolactone, tetra-C ₁ -C ₆ -alkylurea and N, N'-dimethylethylene and N, N'-dimethylpropyleneurea are optionally used Can be added. The proportion of dipolar aprotic solvent in the total solvent used is, for example, 0-50% by weight. Preferably this proportion is 0-20% by weight, particularly preferably no dipolar aprotic solvent is present or the proportion is 0.01-10% by weight.

Based on 1 mol of the adipic acid ester of the formula (II), it is possible to use, for example, 500-5000 ml of solvent. Preferably this amount is 800-3000 ml, especially 1000-2000 ml.

In the reaction with the adipic acid ester of the formula (II), it is possible to use the alkoxide of the formula (III), for example as a dry, preferably finely divided solid, or as an alcoholic solution in which the respective alkoxide is present. it can. Preferably this method is directed to alkoxides
l Each alkoxide is used in an alcoholic solution in which it is present, and the alcohol is worked up in such a way that the reaction with the adipic ester of the formula (II) is distilled off before it significantly begins. In this way, a dispersed suspension of finely divided alkoxides is formed in the reaction mixture, which gives particularly good results. The handling of powder-forming and hygroscopic solid alkoxides is therefore avoided because of these reasons and their corrosive action, requiring special operational safety measures.

Based on 1 mol of the adipic acid ester of the formula (II), it is possible to use, for example, 0.1-10 equivalents of the alkoxide of the formula (III). In this connection, 1 mol of the alkoxide of the formula (III) in which M = alkali metal corresponds to 1 equivalent, and 1 mol of the alkoxide of the formula (III) in which M = alkaline earth metal corresponds to 2 equivalent. . Preferably 0.5-2 equivalents of alkoxide are used per mole of adipate, especially 0.95-1.05 equivalents of alcoholate per mole of adipate.

The adipic acid ester can be reacted in the temperature range of, for example, 80-200 ° C. Preferably 100-15
The temperature range is 0 ° C. The boiling point of the particular inert solvent used is particularly preferably used. It is advantageous to continuously distill off the alcohol formed by the reaction of the adipic acid ester with the alkoxide.

In order to ensure good stirrability during all steps of the reaction, it is also possible during the reaction to add further inert solvents and / or dipolar aprotic solvents of the type described above, if appropriate. .

The alcohol formed by the reaction of the adipic acid ester with the alkoxide, if not already distilled off in the reaction, is distilled off after the reaction is complete. The almost alcohol-free reaction mixture containing the formed cyclopentanone-2-carboxylic acid ester salt of formula (IV) is then reacted with an alkylating agent of formula (V).

Suitable alkylating agents of formula (V) are those wherein R ¹ is methyl, ethyl, n-propyl, i-propyl, benzyl,
It represents 4-chlorobenzyl or 4-fluorobenzyl, and X represents chlorine, bromine or p-tolyl sulfonate. Preferably R ¹ is methyl, ethyl, i-
Represents propyl or 4-chlorobenzyl, and X represents chlorine. Especially methyl chloride is used.

The alkylation can be carried out in the same reaction vessel in which the adipic ester reacts with the alkoxide.
If a volatile alkylating agent of the formula (V) is used, it is advantageous to work under pressure or in a closed tank. The mixture containing the cyclopentanone-2-carboxylic acid ester of formula (IV) can then, if appropriate, be transferred to a reaction vessel suitable for treatment under pressure.

Based on 1 mol of the adipic acid ester of the formula (II) used initially, it is possible to use, for example, 1-20 mol of the alkylating agent of the formula (V). Preferably this amount is 1-10 mol, especially 1-5 mol.

The reaction temperature for the alkylation is, for example, 0-250 ° C.
Range. It is preferably in the range of 20-200 ° C, particularly in the range of 50-160 ° C. The particular temperature optimum for a particular alkylating agent can be readily determined, if desired, by routine testing.

It is advantageous to distill off the solvent (s) present and the excess alkylating agent from the reaction mixture, for example after alkylation.

Isolation of the 2-alkyl-cyclopentanone-2-carboxylic acid ester of formula (VI) formed is not necessary.

Strong organic and inorganic acids, for example, have the formula (VI)
Suitable for treating 2-alkyl-cyclopentanone-2-carboxylic acid esters of Preferred are hydrobromic acid, sulfuric acid, alkylsulphonic acids and arylsulphonic acids. Sulfuric acid is particularly preferred.

The acid is conveniently used in the form of an aqueous solution, for example a 5-99% by weight aqueous solution. Preferably the acid concentration is
It is between 10 and 80% by weight, in particular between 20 and 50% by weight.

Based on 1 mol of the adipic ester of the formula (II) used initially, for example 1-10, preferably 1-5
Equivalent amounts of acid can be used.

Hydrolysis and decarboxylation can be carried out, for example, with 50-150
It can be performed in the temperature range of ° C. Preferably the boiling point of the aqueous reaction mixture is used.

The 2-substituted-2-cyclopentanone of formula (I) produced can be isolated from the reaction mixture, for example by azeotropic distillation.

A preferred embodiment of the process of the invention is carried out as follows: introducing an inert solvent and an alcoholic alkoxide solution. The adipic ester is then added and the excess alcohol and alcohol formed during the reaction with the alkoxide are distilled off. After the reaction is complete, the alkylating agent is added and after the alkylation is complete, the inert solvent is distilled off. Strong acid is added to the residue and the mixture is refluxed. The 2-substituted cyclopentanone is then isolated from the reaction mixture by azeotropic distillation. The method of the present invention comprises converting a 2-substituted cyclopentanone of the formula (I) from an adipate of the formula (II) without isolation of an intermediate, without a drying step, without multi-step solvent removal, without solvent change, And it enables to manufacture without complicated separation operation. The yield in this case is very high, generally above 80% of theory. The method of the invention is therefore energy-saving and especially economical.

The 2-substituted cyclopentanones of the formula (I) are valuable intermediates for the production of insecticides, in particular fungicides (EP 329 397, A-378 953 and A). -
See 537909). They can also be used as perfumes or fragrances, either on their own or after further conversion.

[0049]

Example 1 348.4 g of dimethyl adipate, 381 ml of 30% by weight sodium methoxide solution in methanol and 2884 ml of toluene were introduced into a 3 liter 4-necked flask and methanol was distilled for 2.5 hours. Removed. The mixture is then heated and a mixture of methanol and toluene is added to 100
It was distilled off at a distillation temperature of ° C for 1.5 hours. The residue was transferred to a 3 liter stainless steel autoclave, charged with 50 g of methyl chloride and the mixture heated to 140 ° C. 1
After an hour an additional 50 g of methyl chloride was injected and after 2 hours 52 g of methyl chloride was injected. The mixture is then 150 ° C
It was further stirred for 5 hours.

The batch was cooled and transferred to a 3 liter 4-necked stirred flask apparatus equipped with a distillation column. Most of the toluene distilled at atmospheric pressure, and the rest at 33 mbar.
Distilled at a minimum temperature of 90 ° C. 981 g of 20% by weight sulfuric acid was added to the remaining suspension and the mixture was refluxed for 7 hours. The product was azeotropically distilled off via a water separator (distillation temperature at atmospheric pressure: 92-100 ° C.). 212.5 g of water-clarified product were obtained, containing 77.7% by weight of 2-methylcyclopentanone and 22% by weight of water. The yield was 84.2% based on the dimethyl adipate used.

If desired, water can be removed from the resulting 2-methylcyclopentanone by extraction and / or distillation.

The main aspects and features of the present invention are as follows.

1. formula

[0054]

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Wherein R ¹ is a straight-chain or branched C ₁ -C ₆ -alkyl, C ₃ -C ₇ -cycloalkyl, or unsubstituted or halogen-substituted C ₇ -C ₁₂ -aralkyl 2- A process for producing a substituted cyclopentanone, comprising the formula:

[0056]

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Wherein the ^two R ² are the same or different and each is halogen and C ₁ -C ₆ -alkyl, C ₁ -C
Linear or branched C ₁ -C ₁₀ -alkyl, C ₇ -C, optionally substituted with up to three identical or different substituents selected from the group consisting of ₆ -alkoxy and nitro groups. ₁₂ -aralkyl or optionally up to three identical or different substituents selected from the group consisting of halogen and C ₁ -C ₆ -alkyl, C ₁ -C ₆ -alkoxy and nitro groups An adipic acid ester of C ₆ -C ₁₀ -aryl, which may be substituted, is represented by the formula (II
I) M (OR ³ ) _n (III) In the formula, M represents an alkali metal or an alkaline earth metal, R ³ is C ₁ -C ₁₀ -alkyl, C ₃ -C ₁₀ -cycloalkyl or C ₇ -C Represents ₁₂ -aralkyl, and n is M
Depending on the valence of the alkoxide of 1 or 2 is reacted in this manner to give a compound of formula (IV)

[0058]

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Wherein R ² has the meaning given in formula (II) and M represents a monovalent alkali metal or alkaline earth metal, a salt of a cyclopentanone-2-carboxylic acid ester of Got
Without isolation it is of formula (V) R ¹ -X (V) where R ¹ has the meaning given to formula (I), X is halogen, C ₁ -C ₆ -alkyl sulfonate, Or alkylating with an alkylating agent of C ₆ -C ₁₀ -aryl sulfonate, optionally substituted with up to two C ₁ -C ₄ -alkyl groups, thus giving formula (V
I)

[0060]

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Wherein R ² has the meaning given to formula (II) and R ¹ has the meaning given to formula (I) Process as described above, characterized in that the acid ester is obtained and is hydrolyzed and decarboxylated by acid and heat treatment without isolation.

[0062] 2. In formula (II), the two R ² groups are identical and may optionally be substituted by up to two substituents selected from the group consisting of halogen atoms and C ₁ -C ₄ -alkyl groups. Straight or branched C ₁ −
C ₆ -alkyl, benzyl, or phenyl, optionally substituted by up to two substituents selected from the group consisting of C ₁ -C ₄ -alkyl and nitro, having the formula (III) In, M represents sodium, potassium, lithium, calcium or magnesium, and R ³ is linear or branched C ₁ -C ₆ -alkyl, C
Represents _3- C ₇ -cycloalkyl or benzyl, the solvent being an aliphatic or aromatic hydrocarbon having a boiling point of at least 80 ° C. (at atmospheric pressure), or a halogen and / or C
Aromatic hydrocarbons substituted with _1- C ₄ -alkoxy, or mixtures of these solvents are used and are of the formula (III)
Alkoxides are used as alcoholic solutions in which the respective alkoxide is present, and the alcohol is of the formula
Process according to claim 1, characterized in that the reaction of I) with the adipic ester is distilled off before it starts to any significant extent.

3. The method according to 1 or 2 above, wherein a dipolar aprotic solvent is further added to the solvent.

4. 1 to 3 above, characterized in that 0.1-10 equivalents of alkoxide of formula (III) are used per mole of adipic ester of formula (II) and the reaction is carried out in the temperature range of 80-200 ° C. The method described in.

5. As an alkylating agent of formula (V), R ¹ represents methyl, ethyl, n-propyl, i-propyl, benzyl, 4-chlorobenzyl or 4-fluorobenzyl, and X is chlorine, bromine or p-tolyl. Process according to any of the above claims 1 to 4, characterized in that the one representing sulphonate is used.

6. Using 1-20 mol of the alkylating agent of the formula (V) per mol of the adipic acid ester of the formula (II),
Process according to the above 1 to 5, characterized in that the alkylation is carried out in the temperature range of 0-250 ° C., after the alkylation the solvent present and the excess alkylating agent are removed.

7. 7. The method according to 1 to 6 above, wherein the acid treatment is carried out with hydrobromic acid, sulfuric acid, an alkylsulfonic acid or an arylsulfonic acid, and the acid is used in an aqueous solution.

8. 1-10 equivalents of acid are used per mole of adipic ester of formula (II),
The method according to any one of 1 to 7 above.

9. Process according to any one of 1 to 8 above, characterized in that the 2-substituted 2-cyclopentanone of formula (I) produced is isolated by azeotropic distillation

Claims (1)

[Claims] (1) Formula (1) Wherein R ¹ is linear or branched C ₁ -C ₆ -alkyl, C ₃ -C ₇ -cycloalkyl, or unsubstituted or halogen-substituted C ₇
A process for the preparation of a 2-substituted cyclopentanone having the formula —C ₁₂ -aralkyl, which has the formula: Wherein ^two R ^2's are the same or different and each is the same or different up to 3 selected from the group consisting of halogen and C ₁ -C ₆ -alkyl, C ₁ -C ₆ -alkoxy and nitro groups. branch linear optionally substituted or branched optionally substituted group C ₁ -C ₁₀ - alkyl, C ₇ -C ₁₂ -
Represents aralkyl, or halogen and C ₁ -C ₆
-Alkyl, C ₁ -C ₆ -alkoxy and C ₆ -C ₁₀ -aryl optionally substituted with up to three identical or different substituents selected from the group consisting of nitro groups, Adipic acid ester of formula (II) in the presence of an inert solvent
I) M (OR ³ ) _n (III) In the formula, M represents an alkali metal or an alkaline earth metal, R ³ is C ₁ -C ₁₀ -alkyl, C ₃ -C ₁₀ -cycloalkyl or C ₇ -C Reacting with an alkoxide representing ₁₂ -aralkyl, and n representing 1 or 2, depending on the valency of M, thus giving formula (IV) Wherein R ² has the meaning given to formula (II) and M represents a monovalent alkali metal or alkaline earth metal, a salt of a cyclopentanone-2-carboxylic acid ester of
Without isolation it is of formula (V) R ¹ -X (V) where R ¹ has the meaning given to formula (I), X is halogen, C ₁ -C ₆ -alkyl sulfonate, Or alkylating with an alkylating agent of C ₆ -C ₁₀ -aryl sulfonate, optionally substituted with up to two C ₁ -C ₄ -alkyl groups, thus formula (VI) Wherein R ² has the meaning given to formula (II), and R ¹ has the meaning given to formula (I), a 2-alkyl-cyclopentanone-2-carboxylic acid ester of The method as described above, characterized in that the obtained product is hydrolyzed and decarboxylated by acid treatment and heat treatment without isolation.